1. Field of the Invention
This relates to multi-component seal systems for use in the completion and production operations of oil and gas wells wherein the seal assemblies comprise multiple units, each having sub-components comprising sealing elements and backup elements.
2. Description of the Prior Art
Movement of tubing within the sealing bore of in-place seal receptacles in subterranean wells, such as bores of packers, bridge plugs and the like, during completion and production operations in high pressure, high temperature oil and gas wells has been a major cause of damage to seal systems and subsequent diminished performance and sealing integrity of such seal systems. Damage to the seal systems has become a greater problem as a result of the search for new oil and gas reserves wherein the drilling and subsequent completion is in deeper wells involving exposure to extremely hostile high temperature, high pressure environments wherein the well production may contain a significant amount of hydrogen sulfide, carbon dioxide and methane.
Generally, the seal systems in prior art have not been totally suitable for use in wells having high bottomhole temperature and pressures and corrosive fluids have also been found to be defecient when exposed to even less severe environments. Various new elastomeric materials have been used in these sealing systems. A report of the 52nd Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers, Oct. 9-12, 1977, discusses the teaching of a number of the various new elastomeric type materials in relation to their use in packer seal systems. This report, number SPE 6762, discloses the se of three particular polymeric-type materials which can be utilized in packer seal systems. These polymeric materials are commonly sold under trademarks of Teflon, a polymer of tetrafluoroethylene; Ryton, a polymer of polyphenolenesulphide; and Kalrez, a perfluoroelastomer. Another seal system utilizing these polymers to form a seal unit in turn incorporated into a multi-component seal stack is disclosed in U.S. Pat. No. 4,234,197.
The materials used in these seal systems are relatively expensive and despite the improved performance generally offered by such seal systems, unexplained damage has often resulted to the seal elements employed in these seal stacks. Extremely high sticking forces have also been exhibited by the seal assemblies using these three polymeric materials in multi-unit stacks. When seal stacks have been removed from the well, it has been found that individual elements have been totally destroyed and, in some cases, the order of the adjacent elements comprising the seal stack has been rearranged in actual use. Considerable damage has also resulted to the outer sealing surface of the primary sealing elements. Due to the inaccessibilty of the seals during actual operation, the mechanics of such seal damage has been unclear.